"支持加减剩除( + - * / )"

let a=100
let b=20
let sum=a+b
let sub=a-b
let mul=a*b
let div=a/b

echo 'a=' . a
echo 'b=' . b
echo 'sum=' . sum
echo 'sub=' . sub
echo 'mul=' . mul
echo 'div=' . div
